Reporting from Beirut — Heavy fighting was reported Tuesday as Syrian security forces mounted an offensive in the volatile city of Homs, where activists said seven people were killed.

The government said that "armed terrorist gangs" had carried out assaults at a police station, a hospital and on a roadway and tried to assassinate the head of the hospital's emergency room. Authorities confiscated heavy weapons and explosives and arrested more than 100 "wanted men," according to the official Syrian Arab News Agency, or SANA.

The city of more than 1 million in west-central Syria has been a hub of opposition to the rule of President Bashar Assad since antigovernment protests broke out across the country in March.

But opposition activists say attacks by government security forces in Homs and surrounding communities have escalated in recent days. SANA blamed "terrorist" gunmen for the recent violence.

The Syrian government has barred most journalists from entering the country, making it difficult to obtain independent verification of reports of casualties and damage.

Activists have accused Syrian security forces of attacking peaceful demonstrators, prompting some civilians and army defectors to take up arms and resulting in clashes and what some view as a more militarized conflict.

On Sunday, activists reported nine people killed in Homs and "an atmosphere of true war as sounds of explosions were heard in all areas," according to the Local Coordinating Committees, a grass-roots coalition seeking Assad's ouster.

On Tuesday, more than 20 people were injured in Homs, said the coalition, which accused the government of "targeting anything that moves in the streets."

The activists described "continuous shooting," outages of electricity and water, and plainclothes security units "roaming the residential neighborhoods."

Homs also has been the site of a recent series of assassinations, for which each side has blamed the other.

At Homs National Hospital, the government said, authorities discovered an unexploded homemade bomb made of a fertilizer-based explosive in a large soda bottle rigged with a detonator.

Gunmen opened fire on the hospital, the government said, injuring a bus driver. The head of the emergency room, identified as Dr. Ali Ahmad, survived an assassination attempt, SANA reported.

Authorities arrested 144 "wanted men," according to the official account, and seized AK-47 assault rifles, pump-action shotguns and handguns. Also confiscated were cars and motorbikes, all bearing fake license plates, as well as a fully rigged car bomb, the government said.

Almost 3,000 people have died in violence in Syria since March, according to the United Nations. The government says more than 1,000 security personnel have been killed.